1. Field of the Invention
The invention concerns a support structure for the core of a gas cooled high temperature reactor. Such reactors typically consist of a pile or bed of spherical fuel elements, wherein absorber rods may be inserted directly and which are surrounded on all sides by a reflector. The reflector has a roof, a bottom and a cylindrical side reflector consisting of a plurality of graphite blocks. The cylindrical side reflector is enclosed at a distance with a lateral thermal shield. The support structure employs a plurality of compression members arranged in the annular space between the side reflector and the lateral thermal shield.
The side reflector of a so-called pebble bed reactor must be capable of absorbing both the stationary forces of the pebble bed and the non-stationary forces generated by the flow of gas and the insertion of the absorber rods in the pebble bed. High temperature resistant moderator material, such as graphite, must be used in the side reflector, but the properties of this material do not permit exposure to high tensile and bending stresses. The forces of the reactor core must, therefore, be transmitted radially in the outward direction. From there, they are conducted into the reactor pressure vessel. The lateral thermal shield simultaneously serves as the nuclear shield for structural parts located on the outside.
In the transfer of the horizontal forces of the reactor core to the lateral thermal shield, it must be assured that the differential thermal expansions of the side reflector and the lateral thermal shield are not hindered, so that the mutual stressing and the associated thermal stresses of the side reflector and the lateral thermal shield may be avoided. The supporting of the side reflector against the lateral thermal shield must, therefore, be effected by means of elastic supporting elements. These elements are preferably arranged in the annular space between the side reflector and the lateral thermal shield. At the same time, inadmissible displacement of the side reflector must be prevented.
2. Background of the Prior Art
The state-of-the-art is illustrated by a side reflector known from West German Pat. No. 1 261 606. The reflector consists of graphite blocks of a circular cross section, surrounding a cylindrical cavity. A cylindrical thermal shield in turn surrounds the reflector. The side reflector is supported over its entire height by means of elastic compression elements acting in the radial direction against the lateral thermal shield. Each pressure element comprises a threaded nut welded into the lateral thermal shield with a bushing screwed into it. The bushing serves as the bearing surface for a column of flat springs. The compressive force of the flat springs acts on a prop guided within the bushing and is transmitted by said prop by means of two support elements to the side reflector. Even though the known supporting installation is adequate for the satisfactory transfer of radial compressive forces, it is capable of absorbing the axial relative movements of the thermal shield and the side reflector to a limited degree only (i.e. movements transverse to the support structure).